Infections with certain high-risk strains of genital papilloma viruses in humans (HPV)—for example, HPV 16, 18, or 45—are believed to be the main risk factor for the formation of malignant tumors of the anogenital tract. Of the possible malignancies, cervical carcinoma is by far the most frequent; according to an estimate by the World Health Organization (WHO), almost 500,000 new cases of the disease occur annually. Because of the frequency with which this pathology occurs, the connection between HPV infection and cervical carcinoma has been extensively examined, leading to numerous generalizations.
For example, precursor lesions of cervical intraepithelial neoplasia (CIN) are known to be caused by papilloma virus infections [Crum, New Eng. J. Med. 310:880-883 (1984)]. DNA from the genomes of certain HPV types, including for example, strains 16, 18, 33, 35, and 45, have been detected in more than 95% of tumor biopsies from patients with this disorder, as well as in primary cell lines cultured from the tumors. Approximately 50 to 70% of the biopsied CIN tumor cells have been found to include DNA derived only from HPV 16.
The protein products of the HPV 16 and HPV 18 early genes E6 and E7 have been detected in cervical carcinoma cell lines as well as in human keratinocytes transformed in vitro [Wettstein, et al., in PAPILLOMA VIRUSES AND HUMAN CANCER, Pfister (Ed.), CRC Press: Boca Raton, Fla. 1990 pp 155-179] and a significant percentage of patients with cervical carcinoma have anti-E6 or anti-E7 antibodies. The E6 and E7 proteins have been shown to participate in induction of cellular DNA synthesis in human cells, transformation of human keratinocytes and other cell types, and tumor formation in transgenic mice [Arbelt, et al., J. Virol., 68:4358-4364 (1994); Auewarakul, et al., Mol. Cell. Biol. 14:8250-8258 (1994); Barbosa, et al., J. Virol. 65:292-298 (1991); Kaur, et al., J. Gen. Virol. 70:1261-1266 (1989); Schlegel, et al., EMBO J. 7:3181-3187 (1988)]. The constitutive expression of the E6/E7 proteins appears to be necessary to maintain the transformed condition of HPV-positive tumors.
Despite the capacity of some HPV strains to induce neoplastic phenotypes in vivo and in vitro, still other HPV types cause benign genital warts such as condylomata acuminata and are only rarely associated with malignant tumors [Ikenberg, In Gross, et al., (eds.) GENITAL PAPILLOMAVIRUS INFECTIONS, Springer Verlag: Berlin, pp., 87-112]. Low risk strains of this type include, for example, HPV 6 and 11.
Most often, genital papilloma viruses are transmitted between humans during intercourse which in many instances leads to persistent infection in the anogenital mucous membrane. While this observation suggests that either the primary infection induces an inadequate immune response or that the virus has developed the ability to avoid immune surveillance, other observations suggest that the immune system is active during primary manifestation as well as during malignant progression of papilloma virus infections [Altmann et al. in VIRUSES AND CANCER, Minson et al., (eds.) Cambridge University Press, (1994) pp. 71-80].
For example, the clinical manifestation of primary infection by rabbit and bovine papilloma virus can be prevented by vaccination with wart extracts or viral structural proteins [Altmann, et al., supra; Campo, Curr. Top. In Microbiol and Immunol. 186:255-266 (1994); Yindle and Frazer, Curr. Top. In Microbiol. and Immunol. 186; 217-253 (1994)]. Rodents previously vaccinated with vaccinia recombinants encoding HPV 16 early proteins E6 or E7, or with synthetic E6 or E7 peptides, are similarly protected from tumor formation after inoculation of HPV 16 transformed autologous cells [Altman, et al., supra; Campo, et al., supra; Yindle and Frazer, et al. supra]. Regression of warts can be induced by the transfer of lymphocytes from regressor animals following infection by animal papilloma viruses. Finally, in immunosuppressed patients, such as, for example, recipients of organ transplants or individuals infected with HIV, the incidence of genital warts, CIN, and anogenital cancer is elevated.
To date, no HPV vaccinations have been described which comprise human papilloma virus late L1 protein in the form of capsomeres which are suitable both for prophylactic and therapeutic purposes. Since the L1 protein is not present in malignant genital lesions, vaccination with L1 protein does not have any therapeutic potential for these patients. Construction of chimeric proteins, comprising amino acid residues from L1 protein and, for example E6 or E7 protein, which give rise to chimeric capsomeres, combines prophylactic and therapeutic functions of a vaccine. A method for high level production of chimeric capsomeres would therefore be particularly desirable, in view of the possible advantages offered by such a vaccine for prophylactic and therapeutic intervention.
Thus there exists a need in the art to provide vaccine formulations which can prevent or treat HPV infection. Methods to produce vaccine formulations which overcome problems known in the art to be associated with recombinant HPV protein expression and purification would manifestly be useful to treat the population of individuals already infected with HPV as well as useful to immunize the population of individuals susceptible to HPV infection.